1. Field of the Invention
The present invention relates to a telecommunications unit of a telecommunications system, and more particularly to techniques for interfacing with such a telecommunications unit to allow management data to be transferred to and from that telecommunications unit.
2. Description of the Prior Art
In accordance with a known wireless telecommunications system, a geographical area is divided into cells, each cell having one or more base stations, also referred to herein as central terminals (CTs), for communicating over wireless links with a number of subscriber terminals (STs) in the cell. These wireless links are established over predetermined frequency channels, a frequency channel typically consisting of one frequency for uplink signals from a subscriber terminal to the central terminal, and another frequency for downlink signals from the central terminal to the subscriber terminal.
The system finds a wide variety of possible applications, for example in rural, remote, or sparsely populated areas where the cost of laying permanent wire or optical networks would be too expensive, in heavily built-up areas where conventional wired systems are at full capacity or the cost of laying such systems would involve too much interruption to the existing infrastructure or be too expensive, and so on.
In one embodiment, the central terminal may be connected to a telephone network and exists to relay messages from subscriber terminals in the cell controlled by the central terminal to the telephone network, and vice versa. By this approach, an item of telecommunications equipment connected to a subscriber terminal may make an outgoing call to the telephone network, and may receive incoming calls from the telephone network.
However, such a wireless telecommunications system is not restricted to use with telephone signals, but could instead, or additionally, handle any other appropriate type of telecommunications signal, such as video signals, or data signals such as those used for transmitting data over the Internet, and in order to support new technologies such as Broadband and video-on-demand technologies.
FIG. 1 illustrates an example of a known configuration for a subscriber terminal for such a wireless telecommunications system. Some of the details of such a system are discussed in detail in UK Patent Application No. 9724612.8. In the embodiment illustrated in FIG. 1, the functionality of the subscriber terminal is split between outdoor and indoor units. Hence, an outdoor unit 20 containing an antenna and associated RF (radio frequency) electronics is mounted on the exterior of a subscriber's premises 10.
The RF electronics within the outdoor unit 20 are used to translate received downlink signals (i.e. signals received by the subscriber terminal from the base station) from the RF frequency to an intermediate frequency (IF) suitable for transmission to the customer modem unit 30 via the drop cable 35, and similarly to translate received signals from the customer modem unit 30 at an IF into an RF uplink signal (i.e. a signal for transmitting from the subscriber terminal to the base station) for transmission from the antenna provided within the outdoor unit 20.
The customer modem unit 30 may incorporate a “Code Division Multiplexed Access” (CDMA) modem operating at a fixed intermediate frequency, and also includes the electronics required to interface to the one or more items of telecommunications equipment (in this example a computer 50, fax machine 60 and telephone 70) connected to the subscriber terminal. The customer modem unit 30 is located within the subscriber's premises, for example close to the item(s) of telecommunications equipment. Further, the customer modem unit 30 is typically connected via a power cable to a power supply unit 40.
When installing such a subscriber terminal at a subscriber's premises 10, it is necessary for the antenna within the outdoor unit 20 to be aligned with the base station in order to optimise the signal strength for signals passed between the base station and the subscriber terminal. To enable this alignment process to be performed by a single installation engineer, it is known to provide an output pin 25 on the outdoor unit 20, which can be used to output a voltage indicative of received signal strength. The installation engineer can then connect a voltage meter to the pin 25, and monitor variations in the voltage as the antenna is moved. Typically, the antenna will be mounted in a fixed orientation within the outdoor unit, and hence typically the installation engineer will actually move the entire outdoor unit through a range of angles in order to determine the point at which the maximum voltage is output from the pin 25.
One problem with such an approach is that the resolution of the signal output from the pin 25 is relatively low, and hence this inhibits accurate alignment. Further, there is a delay between moving the antenna, and obtaining an output voltage from the pin indicative of the signal strength for the new alignment, due to the time taken to pass the received signal via the drop cable 35 to the customer modem unit 30, where the relevant processing takes place to determine the signal strength, and then outputting the signal strength indication back up the drop cable 35 for outputting from the pin 25 of the outdoor unit 20. Another problem that can occur is corrosion of the pin 25 due to exposure to the environment. Whilst when the outdoor unit is first installed this will not typically cause a problem, if there is any need subsequently to return and re-perform the alignment process, then any corrosion to the pin in the interim period can further degrade the signal output, and further inhibit accurate alignment.
As an alternative to the above approach of antenna alignment, it is also known to connect the customer modem unit 30 via an RS232 serial link 80 to a laptop computer running predetermined alignment software, and for an installation engineer to then move the antenna until an optimum alignment is detected. However, whilst this provides improved accuracy with regard to antenna alignment, it typically requires the presence of two installation engineers, one to move the antenna, and one to monitor the received signal strength on the laptop computer.
In addition to signal strength data required in order to correctly align the antenna, various other forms of management data sometimes need to be extracted from the subscriber terminal, or input to the subscriber terminal, for example to ensure the continued correct operation of the subscriber terminal. Hence, as an example, certain set-up data may need to be input to the subscriber terminal both at the time of installation, and subsequently, in order to correctly set up the logic within the subscriber terminal. Further, when faults are detected with the subscriber terminal, certain diagnostic data will typically need to be output from the subscriber terminal for analysis. Typically, such set-up data and diagnostic data is also retrieved from the subscriber terminal, and input to the subscriber terminal, via the RS232 serial link 80.
However, it will be appreciated that through this approach, it is necessary to gain access to the subscriber's premises 10 in order to perform such set-up and diagnostic activities. Nevertheless, due to the environmental concerns, and in particular corrosion and ingress of moisture, it has been considered impractical to provide a more complex connection block on the outdoor unit 20 in place of the simple pin 25 in order to support input and output of such management data. Hence, the contact pin 25 typically provides a simple, one-way communication path for a voltage to be output from the subscriber terminal.
Accordingly, it would be desirable to provide an improved technique for interfacing with a subscriber terminal in order to allow management data to be input to, and/or output from, the subscriber terminal. A subscriber terminal is just one example of a telecommunications unit with which such an interface technique would be desirable. It would hence be desirable to provide an interface technique which could also be used with other telecommunications units of the telecommunications system, for example a central terminal.